Thank you for contacting Just Answer.
Answer: There are no laws or rules that determine what a private employer can or cannot call its employees. In fact, the employer could change your job title daily, or never give you one at all.
However, if you did not receive all of your pay for the 18 months you worked in a different position, you could try filing a wage claim. It's free to do so, and in most states one is protected from retaliation (ask the state agency).
In CO, here is where you can file the complaint forms: http://www.colorado.gov/cs/Satellite/CDLE-LaborLaws/CDLE/1251569408907
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